Process for controlling a plurality of turbo engines in parallel or tandem operation

ABSTRACT

A plurality of turbo engines ( 1, 2, 3 ) cooperate in a station, and each turbo engine with the drive machine ( 4, 5, 6 ) driving it forms a machine unit, with which a machine controller ( 28, 29, 30 ) is associated. To control these turbo engines ( 1, 2, 3 ) in parallel or tandem operation to observe at least one process variable, which is preset by the station and is common to all turbo engines ( 1, 2, 3 ), the preset, common process variable is set directly to each of the machine controllers ( 28, 29, 30 ), and this preset, common process variable is controlled exclusively via the machine controllers ( 28, 29, 30 ) associated with the particular machine unit.

FIELD OF THE INVENTION

[0001] The present invention pertains to a process for controlling aplurality of turbo engines cooperating in a station in parallel ortandem operation for observing at least one process variable that ispreset by the station and is common to all turbo engines, wherein eachturbo engine with the drive machine forming it forms a machine unit,with which a machine controller is associated.

BACKGROUND OF THE INVENTION

[0002] A process for operating a plurality of turbocompressors connectedin parallel, which are provided each with a surge limit control toprevent surge, is described in EP-B 0 132 487. The turbocompressors arecontrolled jointly by load distribution controllers and individually bya pressure controller each. The load distribution controllers controlthe setting of the compressors among each other such that there areequal distances between the working point and the blow-off line for allcompressors. Only one of the compressors is controlled by its pressurecontroller, whereas the others are adjusted by the load distributioncontrol.

[0003] A process for the optimized operation of a plurality ofcompressors in parallel or tandem operation has been known from EP-B 0431 287. Using algorithms, a combination of machine parameters in whichthe total shaft power of all drive machines becomes minimal isdetermined here for any working point. A higher-level master controlleris used in this process.

[0004] A higher-level master controller, also called master controller,is bound to be always necessary according to the hitherto common stateof the art in case of the tandem or parallel connection of turbo engineswith individual control devices and individual controllers. The mastercontroller has a higher-level task. It determines the necessaryadjusting commands for the individual machine units from the requiredtotal capacity (desired pressure or desired flow of all compressors).Especially in the case of plants of an asymmetric design, the mastercontroller calculates different manipulated variables for the individualmachine controllers. According to the pertinent state of the art, it isemphasized time and time again that there must be only one controllerfor distributing the load among different compressors, which controllerprocesses only one set point and only one actual value, becauseconflicts may otherwise arise in the downstream machine controllers.Each machine unit needs an unambiguous manipulated variable, which iscoordinated with the other manipulated variables such that no conflictscan arise. In case of flow control, the flow may be measured at a singlepoint only. In case of pressure control, the pressure may likewise bemeasured at a single point only. There may also be only a single setpoint for the common pressure or flow controller. Observing this rule isparticularly important especially in case of use as a pressurecontroller for the final pressure or the suction pressure. If eachmachine unit were equipped with a pressure controller of its own, and ifthe set point of the pressure and the actual value of the pressuredeviated even only slightly between the different controllers, which maybe caused even by the analog/digital conversion of the input signalsalone, the controllers of the parallel-connected compressors would workagainst each other such that one controller would slow down the machineand the other would speed it up. The machine controllers with theirdownstream machines work against each other until one of the twomachines reaches the upper or lower limit of capacity. Moreover, themaster controller is a complicated component, whose failure leads to thestoppage of the entire plant.

SUMMARY OF THE INVENTION

[0005] The basic object of the present invention is to simplify thecontrol of this type, to increase the availability of the individualcontrollers and to avoid colliding interactions between the controllers.

[0006] According to the invention a process is provided for controllinga plurality of turbo engines cooperating in a station in parallel ortandem operation to observe at least one process variable, which ispreset by the station and is common to all turbo engines. Each turboengine with the drive machine forming it forms a machine unit, withwhich a machine controller is associated.

[0007] A master controller affecting all turbo engines for controllingthe process variable is done away with in the process according to thepresent invention by the functionality of this process variablecontroller being divided among the individual machine controllers. Thealgorithm for the distribution of the load among the individualcompressors, which takes place exclusively in the master controlleraccording to the known state of the art, is embodied according to thepresent invention in every individual machine controller. The flow, thefinal pressure, the suction pressure, the pressure ratio, thetemperature, the level in a tank, the power of the drive machine or theload distribution of the compressors can be used as the process variableindividually or in a combination. Since storage space and computingpower are available to a sufficient extent with modern hardware, thereare no restrictions in this respect. Due to the elimination of thehigher-level master controller, an existing station can be expanded byadditional machine units without problems. Only a machine unit with amachine controller is to be added, which machine controller contains thesame control and regulation as each of the existing machine units. Noinvestment, operating or maintenance costs arise due to the use of theprocess according to the present invention. The elimination of themaster controller is likewise unlikely to lead to disturbances inoperation in a station. Since there are no higher-level and lower-levelcontrollers, colliding interactions between different controllers areeliminated. The process according to the present invention is applicableto the parallel operation, the tandem operation and the combinedparallel and tandem operation of the turbo engines in a station.

[0008] Further advantages of the present invention will be mentioned inconnection with the following description of exemplary embodiments ofthe present invention and the state of the art, which are shown in thedrawings. The various features of novelty which characterize theinvention are pointed out with particularity in the claims annexed toand forming a part of this disclosure. For a better understanding of theinvention, its operating advantages and specific objects attained by itsuses, reference is made to the accompanying drawings and descriptivematter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the drawings:

[0010]FIG. 1 is a system diagram of a control system for compressors inparallel operation according to the state of the art;

[0011]FIG. 2 is a system diagram of a control system in tandem operationaccording to the state of the art;

[0012]FIG. 3 is a signal flow diagram for the control system accordingto FIG. 1 or 2;

[0013]FIG. 4 is a system diagram of a control system for compressors inparallel operation according to the present invention;

[0014]FIG. 5 is a system diagram of a control system for compressors intandem operation according to the present invention;

[0015]FIG. 6 is a system diagram of a system for surge limit controlaccording to the state of the art;

[0016]FIG. 7 is a signal flow diagram for the control system accordingto FIG. 4 or 5;

[0017]FIG. 8 is a system diagram of a control system for compressors inparallel operation according to another embodiment of the presentinvention;

[0018]FIG. 9 is a system diagram of a control system for compressors inparallel and tandem operation;

[0019]FIG. 10 is a system diagram of a control system for compressors inparallel and tandem operation, where the control of one of thecompressors is faded in; and

[0020]FIG. 11 is a control system for compressors in parallel and tandemoperation, where the control of one of the compressors is faded in,according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Referring to the drawings in particular, FIG. 1 shows threecompressors 1, 2, 3 in parallel operation, which are driven by a turbine4, 5, 6 each acting as a drive machine. One compressor each forms amachine unit with a drive machine. The three machine units areintegrated within one station, which may in turn be part of a pipelinesystem or is bound in a process. The delivery capacity of the compressor1, 2, 3 can be varied by varying the speed of the turbines. As analternative, the turbines may also be replaced with motors with a fixedspeed, and adjustable guide vanes are used with the adjusting drives 7,8, 9 in the compressors 1, 2, 3 or butterfly valves are used in front ofthe compressors (not shown) in this application.

[0022] The compressors 1, 2, 3 are connected by inlet lines 10, 11, 12to a suction-side bus bar 13, which in turn has a connection to asuction-side process 14 or to a pipeline or to a gas storage unit. Onthe pressure side, the compressors 1, 2, 3 are connected via outletlines 15, 16, 17 to a pressure-side bus bar 18, which in turn has aconnection to a pressure-side process 19 or to a pipeline or to a gasstorage unit.

[0023] A station governor level, which presets as the set pointpresetter 20 the set points for the operation of the station, issuperordinate to the entire station. The actual capacity of themechanical equipment, usually the final pressure or the suction pressureof the compressor plant or the flow, is measured with a sensor 22 andtransmitted as an actual value via a signal line 23 to a mastercontroller 24. The set point of the process variable for the entirestation is sent by the set point presetter 20 via a signal line 21 tothe machine controller 24, which calculates the necessary load of theindividual machine units according to a preset algorithm and presets theset point for the speed or the position of the guide vanes or thethrottling fitting for the respective machine controllers 28, 29, 30 viathe signal lines 25, 26 and 27. The machine controllers 28, 29, 30 inturn set the speed of the turbines 4, 5, 6 and the position of thebutterfly valves or suction throttles to this set point.

[0024] The master controller 24 has a higher-level task. It determinesthe necessary adjusting commands for the individual machine units fromthe required total capacity (desired pressure or desired flow) of allthree compressors 1, 2, 3. Especially in the case of plants of anasymmetric design, the master controller 24 calculates differentmanipulated variables for the individual machine controllers 28, 29, 30.

[0025]FIG. 2 shows the case of application for three compressors 1, 2, 3in tandem operation. The design of this station extensively correspondsto that of the station shown in FIG. 1 for the parallel operation. Thedifference is only that the first compressor 1 is connected to the inletline 11 and, via the outlet line 15, to the second compressor 2, andthis is connected via the outlet line 16 and the inlet line 12 to thethird compressor 3. The suction-side bus bar 13 is not present, and theprocess 14 is connected directly to the inlet line 10 acting as asuction line. The pressure-side bus bar is likewise absent, and theoutlet of the third compressor 3 is connected directly to the process 19via the outlet line 17.

[0026] According to the known state of the art, exactly the samestatements apply to the control of compressors in tandem operation as tothe parallel operation. If the compressors 1, 2, 3 are to be run atconstant flow in tandem operation, the master controller 24 determinesthe speeds to which the individual machine units are to be run to reachthe desired flow. If the compressors 1, 2, 3 are run at constant finalpressure or constant pressure ratio, the master controller 24 determinesthe pressure ratio that every individual compressor 1, 2, 3 has to reachin order to reach the required total pressure ratio. It also applies tothe tandem operation according to the general state of the art thatthere may be only one master controller, which receives only one setpoint and one actual value.

[0027]FIG. 3 shows a signal flow diagram for a control system for astation with three compressors 1, 2, 3. The station set point (flow setpoint or pressure set point) is sent via the signal line 21 and aconverter 31 to a variance comparison unit 32. The actual value(measured flow or pressure) reaches the same comparison unit 32 via thesignal line 23 and a converter 33. The difference between the set pointand the actual value is formed in this comparison unit and is sent to astation controller 34. The station controller 34 adjusts its outputvariable until the actual value corresponds to the set point. The outputof the station controller 34 is sent to the signal lines 25, 26, 27 viapercentage setters 35, 36, 37 and converters 38, 39, 40. These signallines 25, 26, 27 connect the station controller 34 to the three unitcontrollers 41, 42, 43. Each unit controller 41, 42, 43 has a converter44, 45 and 46 for the input variable and another input converter (notshown) for the actual value of the machine, typically the speed of thedrive turbine 4, 5, 6, or the position of the inlet guide vanes in guidevane-controlled compressors. The difference between the actual value ofthe machine and the set point of the machine is formed in the comparisonunits 47, 48 and 49 and is sent to the respective unit controllers 41,42 and 43. These in turn now adjust the speed of the turbine 4, 5, 6 (orthe position of the guide vanes) via converters 50, 51 and 52 such thatthe actual value of the machine will exactly correspond to the set pointof the machine.

[0028] The manipulated variable of the station controller 34 is dividedamong the individual machine units in the percentage setters 38, 39 and40. The adjustment law may be linear or nonlinear depending on the needsof the plant. If necessary, it may be dependent on various parameters. Alinear adjustment law, according to which the turbines 4 and 6 are eachto contribute 30% of the total power and the turbine 5 shall contribute40%, shall be assumed for simplicity's sake. Consequently, a factor of0.3 is set in the percentage setters 35 and 37, and a factor of 0.4 isset in the percentage setter 36. Should the station controller 34 callfor 10% more power, the machine set point, which is sent to the turbine4 via the signal line 25, increases by 3%, the machine set point ofturbine 5 increases by 4%, and the machine set point of turbine 6increases by 3%.

[0029] According to FIG. 3, the elements 31 through 40 belong to thecommon master controller 24, the components 44, 47, 41 and 50 belong tothe machine controller 28 of turbine 4 with the compressor 1, thecomponents 45, 48, 42 and 51 belong to the machine controller 29 ofturbine 5 with the compressor 2, and the components 46, 49, 43 and 52belong to the machine controller 30 of turbine 6 with the compressor 3.

[0030] In many applications, the machine controller usually contains anadditional control function. For example, a pressure control circuit maybe designed such that flow controllers, which control the particularflow through the individual machines, are subordinated to the masterpressure controller. Speed controllers, which will then control thespeed, are in turn subordinated to these flow controllers. The flowcontroller associated with the machines is part of the respective unitcontroller 41, 42, 43 in these applications.

[0031] Each turbocompressor needs a surge limit control, which is partof each machine control and whose task it is to protect the compressorfrom operating in the unstable working range. The operation in theunstable working range is called compressor surge. FIG. 6 shows a blockdiagram of a typical surge limit control for a compressor with variablesuction pressure. A compressor 53 is equipped with a suction line 54 anda delivery line 55. A blow-by valve 56 in a blow-by line 57 may beopened in a controlled manner when needed, thus increasing the flowthrough the compressor when the gas consumption by the process issmaller than the minimum allowable compressor flow. A blow-by valve 56,also called surge limit control valve, is actuated via a control line 58by the surge limiter 59, whose input variables are the inlet pressuremeasured with the sensor 60, the inlet flow measured with the sensor 61,the final pressure measured with the sensor 62, and the inlettemperature measured with the sensor 63. Since the surge limiter 59 isusually embodied within the same controller hardware as the machinecontroller (it is an essential part of the machine controller), signalssuch as compressor flow as well as pressure before and after thecompressor are available within the machine controller and can thus bealso used for the load distribution controller and the capacitycontroller.

[0032]FIGS. 4 and 5 show the control process according to the presentinvention for three compressors 1, 2, 3 integrated to form a station inparallel operation and in tandem operation. As was already described inconnection with FIGS. 1 and 2, the compressors 1, 2 and 3 are coupledwith turbines 4, 5 and 6 as drive machines and are driven by these. Thedelivery capacity of the compressor 1, 2, 3 can be varied by varying thespeed of the turbine. As an alternative, the drive turbines may also bereplaced with motors with a fixed speed, and adjustable guide vanes withthe adjusting drives 7, 8, 9 are used in the compressors 1, 2, 3 orbutterfly valves are used in front of the compressors (not shown) inthis case of application.

[0033] The compressors 1, 2, 3 shown in FIG. 4 are connected by theinlet lines 10, 11, 12 to the suction-side bus bar 13, which in turn hasa connection to the suction-side process 14 or to a pipeline or to a gasstorage unit. On the pressure side, the compressors 1, 2, 3 areconnected via the outlet lines 15, 16, 17 to the pressure-side bus bar18, which in turn has a connection to a pressure-side process 19 or to apipeline or to a gas storage unit. According to FIG. 5, the firstcompressor 1 of the compressors 1, 2, 3 connected in tandem is connectedto the inlet line 11 and, via the outlet line 15, to the secondcompressor 2. This is connected to the third compressor 3 via the outletline 16 and the inlet line 12. The process 14 is directly connected tothe suction line 10, and the outlet of the third compressor 3 isdirectly connected to the process 19 via the outlet line 17.

[0034] The master controller is eliminated in the control processaccording to the present invention. The total set point is sent,instead, to each of the machine controllers 28, 29, 30 from the setpoint presetter 20 of the station directly via the signal line 21. Theactual value is likewise sent directly to each machine controller 28,29, 30 via the signal line 23, so that each machine controller 28, 29,30 can perform the necessary calculations on its own and can adjust thedownstream control units just as if a common, higher-level mastercontroller were used.

[0035]FIG. 7 shows the signal flow diagram for a parallel or tandemconnection of three compressors 1, 2, 3 according to the presentinvention. The station set point of the set point presetter 20 isdivided, sent in parallel to three converters 64, 65, 66, and passed onto the comparison units 70, 71, 72. The actual value from the signalline 23 is sent to three converters 67, 68, 69 and passed on to thecomparison units 70, 71, 72. In the percentage setters 35, 36 and 37,which are arranged between the converters 64, 65, 66, the set point isdivided among the individual machine units, comprising the compressors1, 2, 3 and the turbines 4, 5, 6. The difference between the set pointand the actual value is formed in the comparison units 70, 71, 72 and issent to an amplifier 73, 74, 75 each to the controllers 76, 77, 78 ofthe units. The unit controllers 76, 77, 78 adjust in turn the turbinespeed or the guide vanes of the respective compressor 1, 2 or 3 via theconverters 79, 80 and 81. The converters 67, 64, the percentage setter35, the comparison unit 70, the amplifier 73, the unit controller 76,and the converter 79 are common parts of the machine controller 28,which is associated with the machine unit, which is formed by theturbine 4 and the compressor 1. The converters 68, 65, the percentagesetter 36, the comparison unit 71, the amplifier 74, the unit controller77, and the converter 80 are common parts of the machine controller 29,which is associated with the machine unit, which is formed by theturbine 5 and the compressor 2. The converters 69, 66, the percentagesetter 37, the comparison unit 72, the amplifier 75, the unit controller78, and the converter 81 are common parts of the machine controller 30,which is associated with the machine unit, which is formed by theturbine 5 and the compressor 3.

[0036] The actual value and the set point of the process variable may beany variables as inputs of the converters 67 through 66. They arefrequently the flow through the compressors, the pressure before orafter the station, but they may also be the load distribution of thecompressors in tandem or parallel operation. The pressure ratio of theentire station or a temperature or a liquid level in a tank is alsoconceivable.

[0037] The essential difference between the state of the art accordingto FIG. 3 and the present invention according to FIG. 7 is that themaster controller 24 shown in FIG. 3 with the elements 31 through 40 maybe eliminated altogether, and its function is divided among the machinecontrollers 28, 29, 30, which are present anyway. The elements 31through 34 have been eliminated without replacement and are replacedwith three elements 64, 70 and 76; 65, 71 and 77 as well as 66, 72 and78 each. The converters 38 through 46 are eliminated. However, it ismuch more essential that the functionalities being shown are auxiliaryfunctions embodied purely in software in the machine controllers whichare already present anyway.

[0038] The advantages of the solution according to the present inventionover the state of the art shall be described below based on an exampleby comparing the state of the art with the present invention. Threecompressors 1, 2, 3 according to FIG. 2 are operated with a controlsystem according to FIG. 3 in tandem operation (state of the art). Eachof the compressors 1, 2, 3 shall operate at the beginning of the controlprocess with a pressure ratio of 3. The controlled variable shall be thepressure in the pressure-side bus bar 19. The set point shall be 99 barand the actual value 90 bar. The compressors 1 through 3 shallcontribute one third to the total pressure ratio each. The comparisonunit 32 detects a deviation of 9 bar and transmits this to the stationcontroller 34. This station controller 34 increases its power by apercentage that corresponds to an increase in the pressure ratio by 10%from 90 bar to 99 bar, and an increase in the output signal from 45% to50% shall be assumed here as an example. Each of the three machine unitsincreases its power by the same extent until the measured actual valuecorresponds to the set point.

[0039] The function will be the following in a system according to thepresent invention according to FIG. 7. The actual value on the signalline 23 is 90 bar and the set point on the signal line 21 is 99 bar. Viathe converters 67 through 69, all three unit controllers (capacitycontrollers) 76, 77 and 78 receive the same deviation of 9 bar. Each ofthe three unit controllers 76, 77 and 78 reacts in exactly the same wayas the master controller 24 in FIG. 3. Each of the three machine unitsincreases its power by the same extent until the measured actual valuecorresponds to the set point.

[0040] The final pressure is always controlled in the compressors intandem operation with variable suction pressure such that the controlledvariable is the pressure ratio over the entire station, i.e., the tandemconnection of all compressors. The ratio of the pressure ratios of theindividual compressors is also the variable to be controlled for theunit controllers in the case of compressors in tandem operation, whichare run at constant flow.

[0041] It must be assumed according to the state of the art thatproblems may arise if the input controllers for the set point and theactual value of the individual unit controllers have different drifts ordetermine different numerical values for the set point or the actualvalue of the individual machine controllers due to the incrementalanalog/digital conversion. A deviation of the total delivery capacity ofall compressors from the required power will arise in this case.According to the state of the art, this drawback is considered to bereason for the absolute need for a higher-level master controller. Thisdrawback was pointed out already in the introduction in connection withthe use of three individual pressure controllers.

[0042] This problem is solved according to the present invention by theuse of a load distribution controller. This load distribution controlleracts in addition to the unit controller 76 through 78 (capacitycontroller) and uses the same machine controller 28, 29, 30. Only thefunction of the load distribution controller will be described belowwith the use of the prior-art functional groups. The combination ofcapacity controller and load distribution controller will besubsequently described. This load distribution controller has exactlythe same design as the unit controller 76 through 78 (capacitycontroller) according to FIG. 7. However, the set point of a loaddistribution control is the set point of the load percentage of thecompressor and the actual value is the current load. The distancebetween the working point and the stability limit is usually thecontrolled variable in the case of compressors in parallel operation,and the pressure ratio is usually the controlled variable in compressorsin tandem operation. In the case of a load distribution control fortandem operation according to FIG. 7, the actual value for each machineunit is the particular pressure ratio of the particular compressor, andthe set point is the set point of the percentage contributed by theparticular compressor to the total pressure ratio. The actual value ofthe pressure ratio can be determined by dividing the final pressureobtained for the surge limit control by the suction pressure measuredfor the surge limit control. The total pressure ratio is calculated bydividing the station's outlet pressure by the station's inlet pressure.All compressors are usually operated with the same pressure ratio intandem operation, so that the set point is one third of the totalstation pressure ratio for every individual load distributioncontroller. Should the ratio be different for individual machines, ascaling factor may be taken into account within the set point formation.Should the load percentage of the individual machine units depend onadditional process variables, variable scaling factors may beintroduced.

[0043] The load distribution algorithm calculates a partial load foreach of the compressors and, in the case of compressors in paralleloperation, e.g., a preset percentage of the total flow. In tandemoperation, the algorithm presets, e.g., a fixed, preset percentage ofthe total required pressure ratio. The unit controller of eachcompressor now adjusts the individual machine unit to this value.

[0044] If the actual value processed in the controller deviates from theactual value at which the compressor is actually operating in one of thethree unit controllers due to a measurement error or a converter error,all load distribution controllers detect this alleged deviation from theset point of the load distribution, and control this deviation byadjusting all three compressors such that the load distributioncontrollers will see a uniform load distribution. If the converter 67delivers, e.g., a value that is too high by 10% for the actual value ofunit 1, each of the unit controllers (load distribution controllers)associated with each compressor notices this deviation and adjusts itsdownstream control unit by the preset ratio. In the equalized state, themachine unit 1 operates in a stable manner with a load that is too lowby 6.66%, and the machine units 2 and 3 operate in a stable manner witha load that is too high by 3.33%. The consequence of this is animbalance of all three compressors. However, this is smaller than theindividual error of the machine unit in question.

[0045] The system even operates robustly when the set point and theactual value for each machine unit are determined separately and thereare greater deviations between the set points and the actual values ofthe individual controllers as a result. This represents anotheradvantage of the process according to the present invention. Adisturbance in a common actual value measurement affects the operationof all machine units in the station. This also applies to a disturbancein the set point setter. The actual value measurement can be associatedwith every individual machine unit according to this process. FIG. 8shows, e.g., an arrangement with individual actual value measurement.Instead of a common actual value measurement in the pressure-side busbar 18, the actual value (final pressure after the compressors, beforethe compressors or flow through the compressors) can be measured in therespective outlet lines 15, 16 and 17 with sensors, which are connectedto converters 90, 91 and 92. The individual actual values are then sentvia the converters 69, 64 and 65 to the comparison units 70, 71 and 72according to FIG. 7 and are sent to the machine controllers 28, 29, 30.It is also possible to preset the set point individually. Thus, allnecessary functionalities are now individually associated with eachmachine unit. Conversion errors of the set point and actual valuedetermination are compensated in the same manner with the use of thecontrol process according to the present invention as capacitycontrollers (flow controllers, pressure controllers).

[0046] The advantage of such an arrangement is, on the one hand, thateach of the actual value measurements can be associated with one machineunit, and the converters can be supplied with auxiliary energy from thecontrol box of the respective associated machine unit. Furthermore, thecorresponding units of the other machine units are active even in caseof total failure of set point or actual value converters of one machineunit, and they reduce as a result the negative effects of this failure.It is also possible to form the set point and the actual valueseparately for each machine unit. It is advantageous that there are nocommon components any more and only identical machine systems withouthigher-level system parts are used.

[0047] The above-described case shall be mentioned as an example withthe use of the unit controller as a pressure controller. The desiredfinal pressure is 99 bar. The compressors 1 through 3 shall contributeeach one third of the total power currently needed. Each turbine 4through 6 shall contribute for this 20% of the total available powereach. Now let the actual value measurement fail in the delivery line 17of the compressor 3 and furnish an actual value of 0 bar. The turbine 6runs up to its maximum power because of the missing actual value andcontributes 33% of the total power as a result. The pressure rises as aresult in the pressure-side bus bar 18 and so does consequently thefinal pressure of all compressors 1, 2 and 3. The two intact measuringmeans in the compressor outlet lines 15 and 16 of the compressors 1 and2 notice this increase and reduce the power of the compressors 1 and 2to the extent that the final pressure of all three compressors 1, 2, 3will again correspond to the set point of 99 bar. A station that iscontrolled according to the state of the art by means of a mastercontroller brings all compressors to 100% power in this case ofoperation. The same thing happens in case of failure of a set point. Amaster controller brings all machines to zero and the entire stationceases to offer any power any longer. In case of a control according tothe present invention, the power of the compressor whose set point dropsto zero will drop the zero, the other two compressor controls noticethis deviation and eliminate it by increasing their own power, so thatthe operation of the station as an entirety is not affected.

[0048] The advantage of the solution according to the present inventionis obvious; the master controller can be eliminated, as a result ofwhich costs are saved and the availability is increased. Moreover, thisprocess offers the advantage that a common actual value measurement anda common set point generation are eliminated and both the actual valuemeasurement and the set point setting are associated with eachcompressor unit. Furthermore, it is very essential that the availabilityis increased and the entire plant is less liable to fault.

[0049] Some variants and embodiments for the distribution of the loadamong the individual compressors will be described below.

[0050] It is necessary in many applications to have the possibility ofaffecting the percentage contributed by the individual machine units tothe total load. In some cases, the personnel presetting the operatingcharacteristics of the station may intentionally affect the loadpercentage of individual machine units. If, e.g., a machine unit shallbe put out of operation, it is meaningful to reduce the percentagecontributed by that unit to the total load. This may happen by adding tothe summing unit 70, 71 or 72 a fixed value to offset the equilibrium.The result of this is that the load distribution controller will nolonger load all machine units uniformly, but differently. An example isas follows: Each of the three compressors operates with one third of thetotal pressure ratio in tandem operation without this offset. If anoffset variable of minus 20% is now added to the summing unit 71 (forthe middle compressor), the three machine controllers will makeadjustments until the pressure ratio of the middle compressor becomesexactly 20% smaller than that of the other two.

[0051] Another possibility is to preset the set point individually anddifferently for the load distribution for each of the compressors. Thismay be necessary, e.g., when there is an asymmetry in the machine units.For example, machine units of various sizes may operate together in onestation. The factor must be adapted to the size of the machine units inthis case.

[0052] Another possibility is for an optimizing algorithm to determine acombination of the machine load of the individual machine units that isoptimal for the particular working point. Such optimizing algorithms aredescribed, e.g., in EP-B 0 431 287, which was mentioned in theintroduction. If the present invention is applied to this prior-artprocess, a higher-level computer and master controller may be eliminatedeven in the prior-art process if the algorithm is programmed in eachmachine controller.

[0053] Another need for interfering with the selection of the loaddistribution among the individual machine units may also be encountered,e.g., when a limit of the permissible operating range is reached at oneof the components. If, e.g., gas turbines of various designs are used asdrive machines for compressors, one of the gas turbines may havereached, e.g., the maximum exhaust gas temperature, while the other gasturbines still have reserves for adjustment. The present inventionoffers two approaches to solving this problem. One approach is that thefactor for the splitting of the load among the machine units that arenot at the limit is changed such that the factors are increased at theratio of the machine units that are no longer available. The factor forthe machine operating at the limit is set to zero as long as the machineis being operated at the limit. However, the process according to thepresent invention also compensates this process without thisintervention. Since the unit being operated at the limit does not offerany power any longer, the capacity controller determines a deviationfrom the set point and increases the power of the other unit such thatthe process variable to be controlled will exactly correspond to the setpoint. The control unit and the point of intervention for all theseoffsetting factors are the percentage setters 35 through 37 and theaddition of a fixed value to the summing units 70 through 72.

[0054]FIGS. 9 through 11 show three parallel-connected compressors ofthe low-pressure stage (LP-A, LP-B, LP-C) with three parallel-connectedcompressors of the medium-pressure stages (MP-A, MP-B, MP-C) and threeparallel-connected compressors of the high-pressure stage (HP-A, HP-B,HP-C) connected in tandem. The control system for the compressor MP-B isenlarged in FIGS. 10 and 11. The usual compressors are equipped with anidentical control system. Each compressor is provided with a surge limitcontrol, which was already described in connection with FIG. 6.Furthermore, a machine controller 85 is associated with each machineunit comprising a compressor and a turbine.

[0055] A sensor for determining the actual value of the final pressureof the station is arranged in the pressure-side bus bar 18. The measuredvalue is sent to a converter 86, which is connected to a comparison unit88 via a signal line 87. In addition, the set point of the finalpressure is sent to this comparison unit 88 by the set point presetter.

[0056] Furthermore, a sensor for determining the actual value of theflow of the station is arranged in the pressure-side bus bar 18. Themeasured value is sent to a converter 89, which is connected to acomparison unit 91 via a signal line 90. In addition, the set point ofthe flow is sent to this comparison unit 91 by the set point presetter.

[0057] A sensor for determining the actual value of the suction pressureof the station is arranged in the suction-side bus bar 13. The measuredvalue is sent to a converter 92, which is connected to a comparison unit94 via a signal line 93. In addition, the set point of the suctionpressure is sent to this comparison unit 94 by the set point presetter.

[0058] The signal line 93 of the suction pressure and the signal line 87of the final pressure are led to a computing site 95, in which the totalpressure ratio is calculated. The pressure ratio may be additionallyrated with a fixed factor or even a factor that depends on othervariables. The factor is ⅓ in the first approach, i.e., all threecompressors are loaded equally. A signal line 96, which is led to acomputing site 97, is branched off after the converter 62 for the finalpressure of the compressor MP-B. A signal line 98, which is likewise ledto a computing site 97, is branched off after the converter 61 for thesuction pressure of the compressor MP-B. The pressure ratio of anindividual compressor is determined in the computing site 97. Thecomputing sites 95 and 97 are connected to a comparison unit 99, inwhich the individual pressure ratio of this compressor MP-B is comparedwith its percentage set point relative to the total pressure ratio(which is rated with a factor).

[0059] A signal line 100 is led from the surge limiter 59 to a computingsite 101. The signal line 100 carries a signal containing the distanceof the working point of an individual compressor. In addition, thecorresponding signals of the other parallel-connected compressors aresent to the computing site 101. The mean value of the distance of theworking points is determined in the computing site 101. The mean valueof the distances is compared with the individual value of a compressorin a comparison unit 102. The comparison units 88, 91, 94 are connectedto a summing unit 104 via signal lines, in which a changeover switch 103each is arranged. The comparison units 99, 102 are connected to asumming unit 106 via signal lines, in which a changeover switch 105 eachis arranged. The summing units 104 are also connected to the summingunit 106.

[0060] Via a signal line 107, in which a manual intervention means 108is arranged, the summing units 104, 106 are connected to the machinecontroller 85, which belongs to a machine unit and performs thefunctions of a capacity, final pressure, suction pressure, flow and loaddistribution controller.

[0061] The control system shown in FIG. 11 also contains additionally amaximum selection means 109 and a minimum selection means 110 in orderto limit the speed and the load of the drive machine or other variables.

[0062] In the control system being shown for the tandem or paralleloperation, the capacity control and the load distribution control of thestation are performed by a single machine controller each which isassociated with each machine unit. Deviations for the capacity control,the load distribution control in parallel operation and the loaddistribution control in tandem operation are formed by the machinecontroller. Three different capacity control algorithms (flow control,final pressure control after the high-pressure compressor and suctionpressure control before the low-pressure compressor) can be selected inthis control system. Since the capacity controller can control only onevariable, the other two deviations of the capacity control are switchedto zero via the switches 103. A mutual interlocking is meaningful here.If, e.g., the flow control shall be active, the deviation for thesuction pressure control and the final pressure control is switched tozero. As an alternative, the set point for the non-active controller mayalso be switched to the actual value. This also causes the deviation tobecome zero.

[0063] The same thing happens if one of the load distributioncontrollers is to be deactivated. The corresponding deviation is simplyswitched to zero. This can be done in an elegant manner by switching theoptimizing variable (actual value of the load distribution) to the setpoint. The same thing also happens when a compressor is out ofoperation. The load distribution controllers of the other compressorssimply assume that the compressors that are out of operation areoptimized and therefore do not affect the load distribution among theother compressors.

[0064] It is also possible to operate the machines exclusively by manualoperation. All deviations are switched to zero for this purpose, i.e.,all controllers are switched off. The manual intervention means shown inFIGS. 10 and 11 can be used to impose an artificial deviation as anactuating variable in a manually controlled manner. The particularmachine controller follows this difference as long as the variable ispresent. Since the controller usually also has an integral behavior(PI—proportional, integral or PID—proportional, integral, differentialcontroller), the integral part of the controller responds to this fixeddeviation in the input by continuously adjusting the output. In aspecial embodiment, this manual adjustment can act only on the integralpart of the controller, so that the proportional (P) and thedifferential percentage (D) do not respond to this manual intervention.As an alternative, the manual adjustment may also be performed byswitching the controller 85 to “Manual.”

[0065] An example shall be described below for illustration. Thecompressors in tandem are called the low-pressure (LP) compressor,medium-pressure (MP) compressor and high-pressure compressor (HP). Theparallel-connected compressors are called A, B, C. It shall be assumedthat the plant is in the flow control mode and all compressors are inoperation.

[0066] The flow set point shall be 2% greater in parallel operation thanthe actual value, and compressor LP-A shall deliver exactly ⅓ of thetotal mass flow, compressor LP-B 5% too little, and compressor LP-C 5%too much. Compressor MP-A and compressor MP-B shall deliver 30% of themass flow and compressor MP-C shall deliver 40%. Each of the HPcompressors shall deliver an equal mass flow.

[0067] In tandem operation, compressor LP-A shall be loaded 2% too low,compressor MP-A shall be loaded correctly, and compressor HP-A shall beloaded 2% too high. Compressor LP-B is loaded correctly, compressor MP-Bis loaded 3% too high, and compressor HP-B 3% too low. Compressor LP-Cshall be loaded at a rate of 29%, MP-C at 36%, and HP-C at 35%.

[0068] The following deviations become established on the summing units:Summing unit of compressor MP-B HP-A HP-B HP-C Capacity +2 +2 +2Parallel +2 0 −2 Tandem −2 +3 −1.7 MP-A MP-B MP-C Capacity (104) +2 +2+2 Parallel (102) +3.3 +3.3 −6.6 Tandem (99) 0 −3 −3.3 LP-A LP-B LP-CCapacity +2 +2 +2 Parallel 0 0 0 Tandem +2 0 +5.1

[0069] The control algorithm now forms the resulting deviation beforethe controllers. The following is obtained from this: HP-A HP-B HP-CCapacity +2 +2 +2 Parallel +2 0 −2 Tandem −2 +3 −1.7 Sum +2 +5 −1.7Capacity +2 +2 +2 Parallel +3.3 +3.3 −6.6 Tandem 0 −3 −3.3 Sum +5.3 +2.3−7.9 Capacity +2 +2 +2 Parallel 0 0 0 Tandem +2 0 +5.1 Sum +4 +2 +7.1

[0070] Despite the sometimes conflicting requirements of the individualcontrol tasks (the capacity controller requires an increase in power,the load distribution controller a reduction), each machine controllerreceives an unambiguous adjusting command in the necessary direction inorder to reach the optimum. An interaction between the differentrequirements is ruled out by design.

[0071] In another embodiment, additional algorithms may be added aswell. The drive machines of one or more compressors may reach, e.g., apower limit. This can be additionally processed in the algorithm suchthat the deviation of the machine controllers of the drive machines,which are being operated at the limit, are brought to zero (as in manualoperation). These drive machines will then not participate in a furtherpower increase any longer. To compensate this effect, the differencebetween the optimal adjusting difference according to the above tableand the actual effective difference can be added to the deviation of theother parallel and tandem compressors. This intervention is thusoptimally compensated as well. The process also functions, of course,for a plurality of limiting controllers per machine unit.

[0072] In another embodiment, the limiting controllers may be switched,as is shown in FIG. 11, via an extreme value selection means (maximumselection or minimum selection means). In addition to theabove-described deviations, deviations for the distances of the workingpoints from the limits are formed, e.g., from the maximum speed and theminimum speed in FIG. 11. In addition, the formation of anotherdeviation each for a maximum limitation and a minimum limitation areshown. The deviations for limitations to maxima are switched to aminimum selection, and the deviations for a minimum limit act on amaximum selection. The effective deviation for the machine controller isthus either the deviation according to the above algorithm or thedistance of the working point from the limit when this distance isshorter. When a limit is exceeded, the output of the max/min selectionmeans 109/110 also always controls the machine unit in case ofconflicting requirements of capacity or load distribution controllersprimarily such that the limit is not exceeded in steady-state operation.

[0073] According to the above example, the power of compressor LP-Cshall be increased by a deviation of 6.3%. However, the drive turbineshall be 3% below the maximum operating speed. The effective deviationis thus limited to 3%. As soon as the turbine has reached the maximumoperating speed, the deviation of the speed limiting control becomeszero and prevents any positive deviation on the machine controller viathe minimum selection. Only negative deviations in the direction of aspeed reduction can occur. When the maximum speed is exceeded, thecontroller of the unit reduces the speed.

[0074] It may be occasionally necessary for the individual controlcircuits (pressure controller, flow controller, load distributioncontroller in tandem, load distribution in parallel) to be set todifferent control parameters, because the path time behavior of thecontrol system is different for the individual controlled variables.This can be achieved in a simple manner by imposing different gainfactors on the particular deviations. If, e.g., the deviation of thepressure controller is multiplied by a factor of 1, the deviation of theflow controller by a factor of 2, and that of the load distributioncontroller by a factor of 3, this causes the circuit gain of the loaddistribution controller to become 3 times that of the pressurecontroller.

[0075] If the controller adjustment time is to be adapted individually,this can be achieved in a simple manner. The variable that is theleading variable can be identified from a comparison of the individualinputs of the maximum and minimum selection with the output. Theposition of the changeover switch for the deviations of the capacitycontrollers and the load distribution controllers makes it possible todetermine which of these controllers is in operation. A selection matrixcan now determine which controller adjustment time shall be effective atwhich controller combination. The controller time constant effective inthe machine controller can now be accurately adjusted adaptively as isrequired by the selection matrix.

[0076]FIG. 11 shows an application with a total of nine controlcircuits. If such a system were composed of nine individual controllersaccording to the state of the art, extensive adjustments and mutualinterlocking, which would prevent individual non-active controllers fromrunning into saturation, would be necessary. Furthermore, there is arisk that the nine controllers will mutually dynamically affect eachother. All these drawbacks are circumvented according to the presentinvention. There is only one machine controller per machine unit. Anyadjustment can be eliminated, and an interaction between controllerscannot occur, either. The machine controllers of the other compressorscannot mutually affect each other, because all machine controllers areset to the same parameters for the same controlled variables. Since allload distribution controllers are optimized with the same parameters,they have the same time characteristic. Consequently, it cannot happenthat individual machines run in different directions and consequentlyagainst each other.

[0077] While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. A process for controlling a plurality of turboengines cooperating in a station in parallel or tandem operation toobserve at least one process variable, the process comprising:presetting at least one process variable common to all turbo engines ofthe station; forming a machine unit of each turbo engine with a drivemachine, with which a machine controller is associated; sending thepreset common process variable directly to each of the machinecontrollers; and controlling the preset common process variable based ona deviation of the preset common process variable and an actual valueassociated with the variable sensed at the particular machine unitexclusively via the machine controllers associated with the particularmachine unit.
 2. A process in accordance with claim 1, wherein the finalpressure of the compressors is used as the process variable.
 3. Aprocess in accordance with claim 1, wherein the flow through thecompressors is used as the process variable.
 4. A process in accordancewith claim 1, wherein the suction pressure of the compressors is used asthe process variable.
 5. A process in accordance with claim 1, whereinthe pressure ratio of the compressors is used as the process variable.6. A process in accordance with claim 1, wherein the load distributionin parallel operation is used as the process variable.
 7. A process inaccordance with claim 1, wherein the load distribution in tandemoperation is used as the process variable.
 8. A process in accordancewith claim 1, wherein the power of the turbines used as drive machinesis used as the process variable.
 9. A process in accordance with claim1, wherein the inlet pressure of the turbines used as drive machines isused as the process variable.
 10. A process in accordance with claim 1,wherein the outlet pressure of the turbines used as drive machines isused as the process variable.
 11. A process in accordance with claim 1,wherein the tapping pressure of the turbines used as drive machines isused as the process variable.
 12. A process in accordance with claim 1,wherein the flow through a turbine used as a drive machine is used asthe process variable.
 13. A process in accordance with claim 1, whereinthe current of an electric drive machine is used as the processvariable.
 14. A process in accordance with claim 1, wherein a pluralityof process variables are combined within a station.
 15. A process inaccordance with claim 1, wherein the output variables of the capacitycontrollers are at the same ratio to one another in order to reach auniform load of all machines.
 16. A process in accordance with claim 1,wherein the set points for the load distribution controllers are at afixed but not equal ratio to each other in order to reach apredetermined, nonuniform load of all machines.
 17. A process inaccordance with claim 1, wherein the factor by which the set points ofthe load distribution controllers deviate from each other is a functionof a process variable in order to reach a desired load of all machines.18. A process in accordance with claim 17, wherein the power of theturbine used as the drive machine is used as the influencing processvariable.
 19. A process in accordance with claim 17, wherein thedistance of a process variable from a limit or any other optimizationalgorithm is determined.
 20. A process in accordance with claim 1,wherein the factor by which the set points of the load distributioncontrollers deviate from each other can be influenced arbitrarily inorder to reach a desired load of all machines.
 21. A process inaccordance with claim 1, wherein set points and actual values are presetand measured jointly for all machine units.
 22. A process in accordancewith claim 1, wherein set points and actual values are preset andmeasured individually for each machine unit.
 23. A process in accordancewith claim 1, wherein one deviation is selected among the deviations ofa plurality of process variables and the other, not needed deviationsare switched to zero.
 24. A process in accordance with claim 1, whereinone deviation is selected among the deviations of a plurality of processvariables, and the set point of one of the non-selected processvariables is switched to zero.
 25. A process in accordance with claim 1,wherein the deviations of all process variables are switched to zero andthat the control is performed manually.
 26. A process in accordance withclaim 23, wherein a machine controller with a proportional part and anintegral part is used and the control is performed manually such thatthe manual intervention acts only on the integral part.
 27. A process inaccordance with claim 1, wherein the deviation of the machinecontrollers of the machine units, which are operated at the upper powerlimit, is reduced to zero, and that the actually effective deviation isadded to the deviation of the other machine units.
 28. A process inaccordance with claims 1, wherein the deviation is switched via anextreme selection.
 29. A process in accordance with claim 1, wherein thedeviations for limitations are switched to a maxima of a minimumselection and that the deviations for a minimum limit act on a maximumselection.
 30. A process in accordance with claim 1, wherein thedeviations for different process variables are multiplied by differentgain factors.
 31. A process in accordance with claim 1, wherein theadjustment time of the controllers is adapted individually such that theprocess variable that is the leading process variable is determined froma comparison of the individual inputs of the maximum and minimumselection with the output and the controller that is in operation isdetermined from the position of changeover switches of the controllersfor the process variables, and it is determined via a selection matrixof control functions which adjustment time shall be effective at whichcontroller combination.
 32. A control system for a plurality of turboengines, comprising: a plurality of turbo engines cooperating inparallel or in tandem and forming a turbo engine station; a machine unitformed by each turbo engine, each machine unit including a drive machinedriving the operation of the turbo engine; a machine controller at eacha machine unit; a station input for at least one process variable tocontrol the turbo engines in parallel or tandem operation, the at leastone process variable being preset by the station and being in common toall turbo engines; connections for setting the preset common processvariable directly to each of the machine controllers with the presetcommon process variable being controlled exclusively via the machinecontrollers associated with the particular machine unit.